Hydrostatic transmissions are used to drive the traction wheels of many vehicles. A large number of these are work vehicles such as sweepers, scrubbers, fork lifts, lawn tractors and the like. Commonly these vehicles are operated at one fixed engine speed, and the travel speed of the vehicle is controlled in infinitely variable progression from zero speed, or neutral, to the maximum designed speed in either forward or reverse travel direction by controlling the hydrostatic transmission.
The vehicles with which we are concerned have a seated driver on board, and the usual means of control is a so-called "heel and toe" foot pedal. It is mounted on a bracket attached to the vehicle floor by a pivot at an intermediate position along the pedal. The driver keeps one foot on the pedal, and can exert downward force at the toe of his/her shoe which pivots the front end of the pedal down and the rear end up and causes the vehicle to move forward, or he/she can exert downward force at the heel of his/her shoe which pivots the rear end of the pedal downward and the front end up and causes the vehicle to move in reverse. The greater the downward movement of either end of the pedal from neutral the greater the speed of the vehicle in the corresponding forward or reverse direction of travel.
The ergonomics of this arrangement need to be considered. A human foot can pivot at the ankle through a certain range of forward and backward movement, and is most comfortable in the mid-range of this movement, or when the sole of the foot is approximately perpendicular to the lower leg. Pushing the toe end of a foot down to a position near its limit of motion and holding it there against a resisting force for an extended period of time is very fatiguing. A conventional hydrostatic transmission control pedal requires that the driver's foot be held in this position for extended periods of time in order to drive the machine continuously at full operating speed. But more force is required to hold down a hydrostatic transmission control pedal than is required, for example, to hold down an automobile accelerator pedal, so in time an aching fatigue develops in the leg muscles that control this foot movement. Drivers of machines having hydrostatic transmissions have complained about this for years.
It might appear that one simple way to reduce this fatigue would be to install the pedal at a greater angle with the floor, so that a driver could push its front end all the way down and at that time have his/her foot and leg approximately perpendicular. But situations arise where extended operations are performed at low speed, and then with such a pedal arrangement the driver's foot would be flexed uncomfortably far back, which also produces fatigue, so a compromise position is used which is not optimum in either mode of operation. A pedal is needed that can provide a comfortable position for a driver's foot in extended operation at one speed, which may be maximum designed speed or may be slow speed.
Another aspect of the matter comes from the fact that different drivers are not all the same height, but may be short, average or tall. A tall driver will have longer arms and legs than a short driver. Vehicle seats are commonly mounted on longitudinal slides to accommodate drivers of various heights. A tall driver will set the seat back to get a comfortable reach for his/her arms to the steering wheel, while a short driver will set the seat forward. These seat settings also result in a tall driver having to extend his/her leg forward to reach the foot pedal, while a short driver will be closer to the pedal and will have his/her lower leg more or less directly over it. As a result of these ergonomic factors a tall driver might prefer having the pedal inclined up to some degree, while a short driver might find a relatively flat pedal to be the most comfortable. The current pedals do not provide for such variations.
Thus there is a long-felt need for a foot pedal that will provide an optimum angle during extended periods of same-speed operation, whether at high or low speed, and that will also provide an optimum angle for drivers of various stature.